1. Field of the Invention
The present invention relates to method and apparatus for forming an HSG-Si (hemispherical grained silicon) layer. More particularly, the present invention relates to a method and apparatus for forming an HSG-Si layer on a wafer in the manufacturing of semiconductor memory devices.
2. Description of the Related Art
In general, semiconductor devices are manufactured by coating a silicon wafer with a thin film having predetermined electrical characteristics, using a semiconductor manufacturing apparatus. The thin film is typically formed on the wafer by executing a series of semiconductor processes such as lithography, chemical and physical vapor deposition, plasma etching, HSG-Si manufacturing processes or the like. The wafer coated with the thin film is used for manufacturing semiconductor devices and chips.
Among the above-mentioned semiconductor manufacturing processes, the HSG-Si manufacturing process is widely used to increase the surface area of a capacitor, thereby increasing the capacitance. HSG-Si is commonly manufactured by depositing silicon under a predetermined deposition condition or by depositing amorphous silicon and transforming the silicon into HSG-Si. These types of HSG-Si manufacturing methods are disclosed in U.S. Pat. No. 5,885,869 (issued to Charles Turner et al. on Mar. 23, 1999) and U.S. Pat. No. 5,759,895. (issued to Horng-Huei Tseng et al. on Jun. 2, 1998).
FIG. 1 shows a semiconductor processing system 500 for carrying out a conventional HSG-Si manufacturing process. As shown in FIG. 1, the conventional semiconductor processing system 500 includes a process chamber 510. A first heater 520 for heating a wafer 400 is installed in the process chamber 510. The lower surface of the first heater 520 is supported by a support member 522. The wafer 400 is introduced in the process a chamber 510 through a guide slot 514 formed on one side of the process chamber 510, and is positioned on the first heater 520.
A thermocouple 525 for detecting the temperature of the first heater 520 and a current supplying line 523 for supplying a current to the first heater 520 are provided beneath the first heater 520. The thermocouple 525 and the current supplying line 523 are connected to a controller (not shown). The controller supplies the current to the first heater 520 through the current supplying line 523 based on the temperature of the first heater 520 detected by the thermocouple 525, thereby maintaining the temperature of the first heater 520 within a predetermined range.
The wafer 400 is fed into the process chamber 510 by a handler (not shown), and a control section (not shown) operates a valve device 516 to open/close the guide slot 514 so that the wafer 400 can be guided into the process chamber 510.
The process chamber 510 includes a dome-shaped roof 512, and a second heater 521 is installed on an upper portion of the dome-shaped roof 512 in such a manner that it surrounds the dome-shaped roof 512. The radiant heat created in the process chamber 510 by the first and second heaters 520 and 521 is directed to the wafer 400 by the dome-shaped roof 512.
An RF (Radio Frequency) electrode 540 to which an RF current is applied is installed between the dome-shaped roof 512 and the second heater 521. When a gas such as silane, disilane, or the like is injected from a gas injector 530, RF electric waves are irradiated into the process chamber 510 through the RF electrode 540 to activate the gas. The gas injector 530 is connected to a gas supplying line 538, and the gas is supplied to the gas injector 530 through the gas supplying line 538 from a gas source (not shown).
One side of the process chamber 510 communicates with a discharging port 532. The discharging port 532 is connected to a vacuum pump 535 so that a vacuum can be created in the process chamber 510.
A wafer holder 560, which receives the wafer 400 guided toward first heater 520 and places the wafer 400 on the upper surface of the first heater 520, is installed in the process chamber 510. The wafer holder 560 includes a first arm portion 562 disposed at a peripheral portion of the upper surface of the first heater 520, a second arm portion 564 engaged with a wafer holder driving apparatus 570, and a support 566 connecting the first arm portion 562 and the second arm portion 564. Although only one first arm portion 562, one second arm portion 564, and one support 566 are shown in FIG. 1, the wafer holder 560 comprises three or more sets of such components.
The wafer holder driving apparatus 570 comprises a cylinder 572 provided below the process chamber 510. A bellows 580 provides a seal between the cylinder 572 and the process chamber 510 so that the vacuum state of the process chamber 510 is maintained.
A plunger 574 is disposed in the cylinder 572 and is movable in upward and downward directions. A shaft 576 is engaged with the upper surface of the plunger 574, and the upper end portion of the shaft 576 is engaged with the end portion of the second arm portion 564. A hydraulic pressure supplying section 578 supplies hydraulic pressure to the cylinder 572 to move the plunger 574 in the cylinder 572.
In addition, the conventional semiconductor processing system 500 includes a heater moving apparatus 600 for moving the first heater 520 upward and downward. The heater moving apparatus 600 comprises a motor 608 generating a driving force and a lift 610 which is connected to the motor 608 in such a manner that it can move up and down.
The lift 610 is fixed to the lower surface of a bellows cover 620, and moves the bellows cover 620 upward and downward when the motor 608 is operated. The bellows cover 620 includes an upper cover 622 fixedly attached to the bottom of the process chamber 510 and a lower cover 624 which is moved upward and downward by the lift 610. When the lift 610 is moved upward, the upper cover 622 is maintained in a fixed state and the lower cover 624 is moved into the upper cover 622. Further, the support member 522 of the first heater 520 is mechanically connected to the lower cover 624 so as to move together with the lower cover 624, so that the first heater 520 can be moved upward and downward in the process chamber 510.
Hereinafter, the operation of the of the above-described conventional semiconductor processing system 500 for manufacturing an HSG-Si will be explained.
When the HSG-Si manufacturing process starts, the valve device 516 opens the guide slot 514 whereupon the wafer 400 is moved into the process chamber 510 by the handler.
When the wafer 400 has been moved into a position over the upper surface of the first heater 520, the wafer holder 560 is moved upward by the wafer holder driving apparatus 570 to receive the wafer 400, and then is moved downward to position the wafer 400 on the upper surface of the first heater 520. At the same time, the controller applies operation signals to the first and second heaters 520 and 521 so as to operate the first and second heaters 520 and 521. At this time, the temperature of the first heater 520 is about 700 to 750° C., the temperature of the second heater 521 is about 315 to 325° C., and the temperature of the wafer 400 is about 600 to 610° C.
Then, the controller applies operation signals to the heater moving apparatus 600 in order to move the first heater 520 upward to a fust position A in the process chamber 510. Placing the first heater 520 at the first position A in the process chamber 510 improves the efficiency of heating the wafer 400. At the first position A the first heater 520 is at a level corresponding to that of the gas injector 530, and is vertically displaced upwardly from its initial position by about 80 mm.
At this time, the temperatures of the first and second heaters 520 and 521 are maintained constant, but the temperature of the wafer 400 is raised to 615-625° C. due to the heat radiating in the process chamber 510.
Thereafter, the first heater 520 is left at the first position A for about one minute. The time period of one minute is required for removing foreign substances such as moisture from the wafer 400.
After one minute has passed, a gas is injected on the wafer 400. The gas acts as a source for forming HSG-Si on the wafer 400, and for this purpose a reactive gas such as silane or disilane or the like is used. Then, the RF current is applied to the RF electrode 540 so that the RF electric waves are irradiated into the process chamber 510, to activate the source gas.
When the gas injecting process has been completed, the controller operates the heater moving apparatus 600 to move the first heater 520 upward to a second position B in the process chamber 510. Placing the first heater 520 to the second position B in the process chamber 510 accelerates the growth rate of the HSG-Si by raising the temperature of the wafer 400.
At the second position B, the first heater 520 is displaced vertically upward from its initial position by about 100 mm. At this time, the heating temperatures of the first and second heaters 520 and 521 remain constant, but the temperature of the wafer 400 is raised to 625-635° C. by the heat radiating in the process chamber 510. The gas injected on the wafer 400 is thermally decomposed when the heater 520 is at the second position B, whereby the HSG-Si layer is formed on the wafer 400.
After the formation of the HSG-Si layer has been completed, the controller operates the heater moving apparatus 600 to return the first heater 520 to its initial position, and then opens the valve device 516. Then the handler moves into the process chamber 510 and feeds the wafer 400 to the next stage of the semiconductor device fabrication equipment.
However, in the conventional semiconductor processing system 500, the temperature in the process chamber 510 varies as the first heater 520 is moved in the process chamber 510 while the HSG-Si process is proceeding. As it is known that HSG-Si forms best under a uniform temperature condition, the unstable temperature condition occurring due to the movement of the first heater 520 can produce defects in the HSG-Si layer.
Furthermore, the heater moving apparatus 600 for moving the first heater 520 upward and downward renders the overall structure of the apparatus complex, and contributes significantly to the manufacturing cost of the apparatus.
Furthermore, moving the first heater 520 upward and downward during the forming of the HSG-Si layer takes time, thereby detracting from the productivity of the manufacturing process.